An annular stator core includes a plurality of slots formed in the radial direction. Each slot is groove-shaped and opens in an inner circumference of the stator core. A plurality of coils, formed in advance to form closed loops, are inserted into the annular stator core as distributed windings. In this case, the distance between straight portions that are inserted into two slots in each coil needs to be widened in conformance with the groove shape of the slots that extend in the radial direction.
In the prior art, when inserting generally tortoise-shell-shaped coils into the slots of a fixed iron core (stator core), pushing pieces are used to radially push out the straight portions of a coil so that the straight portions are moved along and inserted in the slots (refer to patent document 1). In this case, the two upper and lower end portions of the coil are formed to be V-shaped. Thus, when the straight portions are moved along the slots, the two upper and lower end portions are deformed to approach the fixed iron core. Patent document 1 also describes that the cross-sectional shape of the conductive wire of the coil is not limited to a substantially circular shape and may have a different shape such as a rectangular shape.
A further proposed method for manufacturing a stator inserts first sides (straight portions) of a plurality of coils into a plurality of first slots of a stator core, and then inserts second sides (straight portions) of the plurality of coils into a plurality of second slots, which differ from the first slots, so that the coils are spirally overlapped as viewed from the end face of the stator core (see patent document 2). The method of patent document 2 uses a jig that includes a first holding groove group and a second holding groove group formed on an outer circumference. The first holding groove group includes a plurality of slit-shaped holding grooves that formed at a pitch that is an integral multiple of the pitch of the slots of the stator core. The second holding groove group is formed at the same pitch as the first holding groove group. The first sides of the plurality of coils, which are wound in advance, are respectively inserted to the first holding groove group, the second sides are respectively inserted into the holding grooves of the second holding groove group that are adjacent to the holding grooves into which the first sides are inserted. Then, each coil is arranged along the circumference of the jig. The jig is inserted to the inner circumference of the stator core. Subsequently, the first side of each coil is pushed toward the outer side in the radial direction by a pushing means and inserted into the corresponding slot of the stator core. Then, the jig is rotated by a predetermined angle relative to the slot of the stator core and positioned so that the second holding grooves are aligned with the corresponding slots of the stator core. Subsequently, the second sides are pushed toward the outer side in the radial direction by the pushing means and inserted into the corresponding slots of the stator core.